I went through US pre-clearance in AUH on 10/20 (well technically 10/21 as it was 1AM) as well and had no issues. My experience:

• Security was a giant pain in the .... While the line was very short, just a few minutes, (both priority and economy), it was one of the more thorough screenings I've had in a while. Everything off and out of your bag, all devices must be powered on, etc. Interestingly security is staffed with UAE locals, not people from the US
• Global Entry didn't help at all as after you got your receipt, you still had to wait in line to see an immigration officer. Instead of having one immigration agent dedicated to folks coming through GE, you get mixed in with pax holding foreign passports which can take forever. DHS/ICE really needs to get their act together and streamline the process for GE folks
• I was a transfer pax as well and I only went through security at US Pre-clearance, I don't recall a security screening for transfer pax
• Despite all this, I was still through in about 15-20 minutes so not really any worse than going through customs/immigration in the US, except for the whole strict security screening